1. Field of the Invention
This invention relates to sealing subterranean zones penetrated by well bores using high density polymeric sealing compositions.
2. Description of the Prior Art
Wells which produce oil and/or gas very often also produce water. If the amount of water produced is low, the water can be separated from the oil and/or gas in an economical manner. However, if large quantities of water are produced by a well in addition to oil and/or gas, the cost of pumping, handling, storing and disposing of the produced water often makes the operation of the well uneconomical.
Polymeric compositions which form polymerized and cross-linked impermeable masses have been developed and used heretofore in well completion and remedial operations. For example, polymeric compositions have heretofore been used to reduce or terminate the flow of water from a subterranean zone penetrated by a well bore. Such compositions are introduced into a subterranean water producing zone and caused to polymerize and cross-link therein whereby a stable gel which reduces or terminates the water flow from the zone is formed therein. U.S. Pat. Nos. 3,334,689 issued Aug. 8, 1967 and 3,490,533 issued Jan. 20, 1970, both to McLaughlin, disclose polymerizable monomer solutions containing a polymerization catalyst for injection into subterranean zones. The solutions polymerize and are cross-linked in the zones to form stable gels which reduce the water permeabilities of the zones and decrease or terminate the flow of water therefrom.
U.S. Pat. Nos. 5,335,726 issued on Aug. 9, 1994 and 5,358,051 issued Oct. 25, 1994, both to Rodrigues, disclose methods of forming polymeric gels in subterranean zones to reduce or shut off the flow of water therefrom wherein a monomer is polymerized in the formation in the presence of a cross-linker by an initiator selected from certain azo compounds. Also, the use of hydroxy unsaturated carbonyl monomers is disclosed.
The aqueous polymerizable monomer solutions containing monomer or monomer and cross-linker and a polymerization initiator have heretofore been pumped as low viscosity solutions into subterranean zones in which sealing procedures are to be conducted. The low viscosity solutions polymerize after placement which results in the formation of sealing gels in the zones. The polymerization of the monomer solutions is not initiated by the polymerization initiators heretofore used and/or does not proceed at an appreciable rate until oxygen-induced polymerization inhibition is overcome. That is, a polymeric solution contains dissolved oxygen which inhibits the polymerization of the monomer in the solution until all of the oxygen is consumed. The time required for the initiator to react with the oxygen present in the solution is known as the "induction period." The induction period enables placement of the polymeric solution in the zone to be sealed before polymerization of the solution prevents its flow into the zone.
While various polymerization initiators such as persulfates, peroxides, oxidation-reduction systems and azo compounds have been utilized heretofore, azo compounds are generally preferred for the reason that they are less likely to cause premature gelation. Persulfates, peroxides and oxidation-reduction systems are subject to premature activation when they contact certain reactants such as ferrous ion.
In some wells, undesirable gas and/or water is produced into the well bore from subterranean zones penetrated thereby which makes the drilling of the well bore very difficult. For example, offshore wells in deep seawater are often drilled in a manner whereby the well bore is open to the sea floor. As a result, gas and/or water which flows into the well bore from subterranean zones cannot be controlled. That is, since the well bore is open, it cannot be isolated whereby a sealing composition can be pumped into the gas and/or water producing zones under pressure, i.e., the sealing composition cannot be squeezed into troublesome subterranean zones. Even in wells where pressure pumping operations can be carried out, it is often difficult to place a sealing composition in a subterranean zone because of its location, e.g., when the zone is near the bottom of the well bore.
Thus, there are needs for improved subterranean zone sealing compositions and methods which can be utilized in offshore well bores which are open to the sea floor as well as in other well bore sealing applications.